Numpy: ndarray does not accept memoryview for buffer= under python2

[navytux]

Hello up there.

I've discovered that ndarray(buffer=memoryview) fails on python 2:

In [1]: sys.version
Out[1]: '2.7.10 (default, May 26 2015, 13:16:40) \n[GCC 4.9.2]'

In [2]: numpy.__version__
Out[2]: '1.10.0.dev0+9e7a0b2'


In [3]: b = bytearray([1,2,3])

In [4]: b
Out[4]: bytearray(b'\x01\x02\x03')

In [5]: m = memoryview(b)

In [6]: m
Out[6]: <memory at 0x7fa1f4e59b50>

Creating ndarray backed by memoryview fails:

In [7]: a = ndarray((3,), buffer=m, dtype=uint8)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-32-1528204f5358> in <module>()
----> 1 a = ndarray((3,), buffer=m, dtype=uint8)

TypeError: expected a readable buffer object

though it succeeds if we pass memoryview to array():

In [8]: a = array(m, copy=False)

In [9]: a
Out[9]: array([1, 2, 3], dtype=uint8)

In [10]: a[0] = 5

In [11]: a
Out[11]: array([5, 2, 3], dtype=uint8)

In [12]: b
Out[12]: bytearray(b'\x05\x02\x03')

[7] works on python 3, of course.

Thanks beforehand,
Kirill

[charris]

IIRC, we decided not to support memoryview in Python 2 because it was only available for 2.7. However, it has been backported to 2.6 and we no longer support earlier versions, so we should probably revisit that decision.

[navytux]

Yes. Please note it is already supported on Python 2 - array() accepts memoryview ([8-12] above). Only ndarray constructor does not accept memoryview for buffer= argument.

[akochepasov]

We'd love to have better support for memoryview as well

[rgommers]

Closing this, Python 2.x only issues are no longer relevant given that we're dropping support for 2.7 soon.